There is provided an improved process and apparatus for extracting organic substances from a solid material and more particularly an improved process and apparatus for extracting hydrocarbons from hydrocarbon bearing ores such as diatomaceous earths and the like.
Many earth formations contain deposits having substantial amounts of hydrocarbons. Oil bearing diatomaceous earths, oil shale, bitumens, resins of fossil origin, tar sands and natural asphalts all contain varying degrees of hydrocarbons.
A variety of extraction processes for removal of oil from oil-bearing ores have been proposed. These may be roughly divided into the following categories: pyrolysis or coking; aqueous extraction and solvent extraction.
Illustrative of a process in the first category is the TOSCO process where mined crushed oil shale is preheated to about 500.degree. F. and fed to a slanted, rotating drum, where it mixes with marble-sized ceramic balls preheated to 1600.degree. F. The hot ceramic balls pulverize and heat the shale until oil and gas boil off. The spent shale is subsequently screened out and the oil vapors condensed and fractionated to provide naphtha, gas and oil.
Aqueous processes using steam or hot water have also been described. Exemplary of this category is a hot-water steam extraction process for oilsands consisting of the steps of conditioning, primary separation and air flotation. Hot water, steam and a base are used to form a pulp with the oilsand in the conditioning step. The effluent from the conditioning step is screened and additional water is added prior to passage to the primary separation step, where gravity allows solids to settle. Air flotation is used to remove bitumens which do not settle in the primary separation stage.
The literature discloses a number of solvent extraction processes, many of which employ water as well as a solvent. For example, U.S. Pat. Nos. 4,239,617 and 4,167,470 issued to Karnofsky describe a process which attempts to recover petroleum crude oil from oil laden diatomite by a continuous stagewise countercurrent extraction-decantation process. Ore is extracted by countercurrent decantation with a hydrocarbon solvent. Solvent is recovered from the extract by multiple effect evaporation followed by stripping. The spent diatomite is contacted with water and solvent is recovered from the resulting aqueous slurry of spent diatomite by steam stripping at superatmospheric pressure.
J. H. Cottrell, "Development of an Anhydrous Process for Oil-Sand Extraction", published in M. A. Carrigy, ed., Athabasca Oil Sands: A Collection of Papers, Edmonton, Alberta: Research Council of Alberta, 1963 (hereinafter referred to as the Cottrell article) discloses an anhydrous solvent extraction process using a three stage drain circuit to extract hydrocarbons from water-wet Athabasca oil sands. Process conditions are controlled to ensure that the inner film of water coating the sand particles and surrounded by a bitumen film is maintained in order to enhance the free flow of hydrocarbons through an oil sand bed. This was explained under the theory that the apparent diameters of the solid-water particles randomly laid down in the draining step were quite uniform and were larger than those of most dry solids existing within a given oil-sand sample.
In a commercial plant proposed in the Cottrell article oil sand and hydrocarbon solvent would be mixed in a mixer and then passed as a slurry on a moving belt through three consecutive drains. A mixture of solvent and hydrocarbon would pass through the slurried bed in each drain under appropriate process conditions to maintain the water film. Solvent would subsequently be recovered from the spent slurry by steam stripping and from the raw bitumen product recovered from the first drain by fractionation.
These and other prior processes suffer from one or more of several defects or limitations. For example, many prior processes fail to adequately mate process yields with process energy requirements. Other processes fail to make economical and efficient use of solvents, particularly in extracting the hydrocarbons from the hydrocarbon bearing ore. There are also problems involved in efficient recovery of any solvents used as well as reduced efficiencies due to the logistics and mechanics of removing large amounts of solids and problems associated with the presence of fines including fines removal from product streams. These and other defects or limitations are substantially minimized if not eliminated by the present inventive method and apparatus.